Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual integrated circuit chips. A common technique for forming the circuitry on a semiconductor is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by inconsistencies or unevenness in the wafer surface. The need for a precise image projection is accentuated with the current drive toward smaller, more complex integrated circuit designs. Semiconductor wafers are also commonly constructed in layers, where a portion of a circuit is etched on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on the wafer, an oxide layer is put down that allows the vias to pass through the oxide layer while covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer as it is constructed. These imperfections are preferably smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad that is moving in the plane of the wafer surface to be planarized. When the polishing pad contacts the wafer surface, material is removed from the wafer thereby polishing the surface. In general, the three primary objectives of the CMP system are: (1) to planarize the surface of the wafer by removing portions of material that extend above the surface of the wafer; (2) to uniformly remove material from the entire surface of the wafer; and (3) polish the surface of the wafer to remove scratches or other defects.
The polishing pads commonly used in this process include both belt-type pads and rotary-type pads. A. belt-type pad typically consists of one or more sections of material that are joined together to form a belt. The belt is placed around a plurality of rollers that cause the belt to rotate in a linear path. The rotating belt can then be brought into contact with the wafer to polish its surface. A rotary-type pad typically consists of one or more sections of material that are joined together to form a pad. The pad is attached to a rotary machine that rotates the pad to polish the surface of the wafer. A polishing fluid, such as a chemical polishing agent or slurry containing micro abrasives, can be used in conjunction with the polishing pad. The slurry is disposed between the polishing pad and the wafer and enhances the polishing of the wafer.
In polishing a wafer, the type of pad used, the slurry used, and other polishing parameters can be changed to produce different polishing results. For example, the hardness, stiffness, and construction of the polishing pad can be changed to effect the polishing. Also, the slurry used to polish the wafer, the polishing time, and the polishing pressure can also be varied.
The makeup of the wafer that is to be polished often dictates how the polishing parameters are selected. Different wafers and different layers within a wafer can have different compositions such as different materials, different patterns, and different pattern densities. Each of these different compositions can affect the polishing of the wafer and a specific combination of polishing parameters may be preferred for polishing a wafer that has a certain composition. Thus, selecting a combination of polishing parameters that will produce a desired result is important. However, current systems do not allow for an efficient and effect method of determining an optimum set of polishing parameters to achieve a desired polishing result. A method and system that overcomes these deficiencies is needed.